Many applications of belts for transporting materials and transmitting power require a belt that will remain precisely positioned and permanently tensioned when operating on pulleys or rollers that are located on fixed centers. When two or more belts must operate on pulleys or rollers arranged on shafts having fixed centers the positioning and tensioning of the belt for satisfactory operation is very important. The use of fixed centers to conserve space and reduce cost by eliminating take-up mechanisms is very common in machine design today, particularly in the business machines field.
Endless belts in a variety of forms have been produced to serve this purpose.
One design utilized plied stitched belts in which two or more plies of woven fabric were stitched together. Such belts tended to delaminate and did not possess the elasticity nor the elastic recovery necessary to maintain permanent tension on the fixed center drive.
Another design used gimped yarns (yarns with a rubber core) in a woven fabric. This product generally afforded high, but uncontrollable elasticity so that tension on the drive varied tremendously and was ineffective.
Another design used unsupported elastomeric film, but this belt, because of the lack of any fabric reenforcement to contain its elastic properties, exhibited excessive creep, high abrasive wear and consequently poor operating characteristics.
A popular design today embodies a woven tubular fabric where a degree of elasticity has been imparted through the weave pattern. This has been a successful design but weaving limits the elasticity and it is not possible to impart sufficient elasticity to meet the requirements of many of the modern machines.
Furthermore a tubular knit substrate has been used to obtain elastic properties, but the art of knitting tubular fabrics does not produce a material that possesses adequately controlled elasticity and the degree of elasticity is limited by the size of each particular tubing.